Hot water for domestic purposes can be provided at low cost by a solar heater which usually comprises a storage tank, a solar heat collector, and a pump for circulating water through the collector from the storage tank and back to the storage tank. The heat collector usually takes the form of a flat plate of blackened metal, which is exposed to sunlight, and to which tubes are attached in any manner which provides good thermal contact. The tubes are connected to headers at each end of the collector plate. The collector is usually provided with a glass or a transparent plastic cover to trap the heat from the sun, and to reduce the heat loss to the atmosphere. The storage tank is connected to the collector by suitable pipelines, and water is circulated through the collector by an appropriate pump, thereby to provide hot water in the storage tank.
It is most desirable when the temperature of the water in the collector drops below the temperature of the water in the storage tank that the pump be de-energized to avoid circulating water into the storage tank which is cooler than the water already in the tank. This feature is provided by the control module of the system of the invention which senses when the collector temperature drops below the temperature of the contents of the storage tank to de-energize the pump motor, and which also senses when the temperature of the water in the collector is above the temperature of the water in the storage tank, so as to start-up the system.
It also is desirable that the collector be protected from the effects of freezing of the water contained therein. The valve module of the system of the invention responds to electrical commands from the control module to drain the water out of the collector should the temperature of the water in the collector approach freezing temperatures. The control module in the system of the invention also senses the temperature of the water in the storage tank, and shuts down the pump and drains the water out of the collector whenever the temperature of the water in the storage tank reaches a predetermined maximum level. The valve module is spring loaded, and the electrical connections are such that in the event of a power failure the valve module drains the collector.